The invention relates to electronic circuitry concerning timing signals and their production and distribution; oscillators as sources of such as timing signals; and communications according to timing signals.
Digital electronic data processing circuitry and systems require timing signals to synchronise data processing activities. Customarily, such timing signals include a master timing signal from which other timing signals can be derived. Such a master timing signal is commonly referred to as a xe2x80x98clockxe2x80x99 signal. It is often desirable to have a clock signal that is available in more than one phase.
An example of a two-phase clock signal is where available clock signals have a phase difference of 180-degrees as often used for dynamic logic and shift register circuitry. An example of a four-phase clock signal is where available clock signals have successive phase differences of 90-degrees. Semiconductor integrated circuits (ICs or chips) are typical host environments, often very large scale (VLSI) chips as for microprocessors or memories.
Historically, modest operating clock frequencies up to about 50 MHz were satisfied by use as off-chip quartz crystal clock oscillator with simple point-to-point on-chip clock signal distribution. Nowadays, at much higher operating frequencies, typically aiming for 300 MHz to 1 GHz, inherent on-chip distribution problems associated with clock signal reflection and skew have become highly significant as binary signal widths/durations are no longer so much shorter than clock signal pulses. Natural progression of IC designs is for chips to become physically bigger and functionally more complex, which compounds these problems.
Clock signal generation is presently typically by frequency multiplication from off-chip crystal clock oscillators using on-chip phase locked loop (PLL) control circuitry which occupies valuable chip area, consumes considerable power, and experiences problems with signal reflections, capacitive loading and power dissipation that effectively limit maximum operating frequency. Related clock signal distribution usually involves tree-like arrangement of operational circuitry with chains of clock signal boosting buffers at intervals. Even so, variability of semiconductor process parameters, including in the buffers, leads to undesirable and unpredictable phase delays (skew) at different positions on the chip, thus can adversely affect reliable synchronous operation and communication even for neighbouring areas of a chip. As a result, ICs often have to be rated and run at lower than maximum designed-for clock rates. Indeed, IC manufacturers are even reversing long-standing trends by use of smaller chip sizes for latest ICs.
The development of ever more comprehensive xe2x80x98systems-on-siliconxe2x80x99 chips is being hampered by lack of viable provisions for reliably clocking large area high-density chips. It is noteworthy that clock rates tend to be limited to less than about 1 GigaHertz despite such as Mosfet IC transistor features being capable of switching at 25 GigaHertz or more.
This invention arises basically from looking for some alternative approach that at least reduces areal and/or power demands of on-chip PLL provisions, if possible further addresses and to some useful extent resolves clock signal distribution problems.
One broad view or aspect of this invention resides in the concept and realisation of method and means for effectively integrating or synergistically combining distribution of repeating pulse or cyclic signals with active means for producing and maintaining those signals. A composite electromagnetic/semiconductor structure is facilitated that simultaneously generates and distributes timing signals, including a master clock. A suitable said signal path exhibits endless electromagnetic continuity affording signal phase inversion of an electromagnetic wave type signal, conveniently with path-associated regenerative means.
A successful inventive rationale aspect hereof has been evolved in which time constant for repeating pulse or cyclic signals is related to and effectively defined by electrical length of said signal path in the signal distribution means. A travelling electromagnetic wave recirculating endlessly electromagnetically continuous said signal path is preferred, when its traverse time of the signal path determines said time constant.
Interestingly and quite surprisingly, this has been found to be conducive to particular inventive direct production of pulse-like cyclic signals inherently having fast rise and fall characteristics, i.e. already xe2x80x9csquarexe2x80x9d as produced, rather than requiring resort to xe2x80x9csquaringxe2x80x9d action on a basic inherently substantially sinusoidal signal as hitherto conventional. Indeed, such inventive electrical length/signal traverse time-constant-defining rationale hereof leads conveniently and advantageously to said electrical length or one said signal traverse effectively first defining one unipolar half-cycle signal excursion and next, or at next said signal traverse, effectively completing definition of a full bipolar cycle comprising two opposite half-cycle excursions. Said electrical length thus corresponds to 180-degrees for each of two successive pulse excursions for such full bipolar cycle.
Specific inventive aspects hereof to achieve such rationale are viewed as involving signals of a travelling wave nature with the signal distribution path involved having a suitably propagating nature therefor, typically of endless transmission-line form, further with transposing effect and inverting action associated with re-circulations of desired signals.
In one specific inventive aspect hereof, desired repeating cyclic signals involve re-circulatory travelling wave propagation means effectively affording rotation thereabout by a desired travelling wave and setting duration of each signal excursion, with active regenerative means that can be of switching and amplifying nature, conveniently bidirectional inverting amplifier, supplying energy requirements and setting relatively short rise and fall at ends of each signal excursion.
Suitable travelling wave propagation means with desired transposing effect relative to active inverting means is exemplified, as seen by the traversing travelling wave, by physical width twisted along its length to connect opposite sides to input and output of the inverting means, say as though a Moebius band or ribbon. Indeed, an integrated circuit made on a flexible substrate could be of elongate form with said path following its length and its ends interconnected as a Moebius band or ribbon, even with functional circuitry blocks to either or both sides of or straddling its travelling wave propagation feature. At least then, integration of inverting and travelling wave propagating features of cyclic signal means hereof could be to the extent of up to all its length being of continuous semiconductor inverter nature, at least using CMOS technology.
However, for planar implementation of travelling wave propagation means, a typical transmission-line form uses spaced path-following conducting features, aforesaid Moebius twist effect being afforded by way of no more than a mutually insulated cross-over of those spaced conducting features. An alternative would be use of a transmission-line inverting transformer in or associated with otherwise transmission-line form of the travelling propagation means.
An inventive aspect of exemplary implementation hereof uses spaced conductive features as trace formations each having substantially the same length and being transposed on the way between output and input of at least one inverter feature connected to, preferably between, those conductive traces. In practice, at least where the inverter feature is of extent less than about 1% along the conductive features, there will preferably be plural inverter features spaced along the conductive features or tracesxe2x80x94unless this invention is adapted to operation as a standing wave oscillator.
Preferred inverter means is of bidirectional nature, such as a pair of opposite inverters side-by-side or back-to-back; and such provision facilitates direct simultaneous production of similar or substantially identical anti-phase cyclic signal components.
Particularly interesting and advantageous results available from this invention include timing signal provision with extremely low power consumption that can effectively be limited to transmission-line and inverter action losses, i.e. to near-negligible topping-up via the inverter provision(s), and take-off to operational circuitry is readily made, e.g. by way of light bidirectional connection paths of passive resistive and/or capacitive and/or inductive or transmission-line nature, or unidirectional say using diodes or inverters, etc as will be described in more detail.
Another such available result is that, at least in principle and absent fabrication imperfections, cyclic signal provision hereof has no innate preference for either direction or rotation of travelling wave propagation, though either may be predisposed or imposed by such as prescribed spacings or other differences between or within inverter means.
Inventive proposals and aspects hereof as to pulse generators and oscillators as such include transmission-line structures using conductive metal and insulating dielectric layers in a manner compatible with IC production generally and particularly together with regenerative circuitry associated with the transmission-line as such, typically and conveniently formed below and connected by vias; required insulated cross-overs or spaced transmission-line transformer parts are likewise readily formed including such as via jump connections for the cross-overs; and resulting advantageously DC unstable interconnection of terminals of such as bidirectional inverters as the regenerative means; synchronous detection and bridge rectifier action of preferred bidirectional inverters; reinforcing sequential action of such bidirectional inverters including recycling electrical energy relative to supplies; etc.
Moreover, there are inventive aspects in interconnection/intercoupling of timing signal generating and distribution circuitry hereof, whether by direct connection or by sharing magnetic and/or electrical fields; and doing so on a self-synchronising basis with extension to different frequencies particularly in odd-harmonic relationship. Intercoupling and coordinating between ICs as such and further with transferring data also have important innovative and inventive merit.
Other aspects and features of the present invention arise later in this Description, and/or are as set out in independent and dependent claims wording of which is to be taken as incorporated here too.